Dendrochronology. It's not a well-known word to most people, but for the researchers at the UA's Tree Ring Research Laboratory, it's a way of life.

Dendrochronology is the dating of past events using tree ring growth records - and the University of Arizona is the world leader.

"This is where people from around the world come to learn this (tree-ring dating). In some fields, this is what the UA is known for," said Malcolm Hughes, the lab's director.

The lab's history is closely tied to the life of its founder, Andrew Douglass, who came to the UA in 1906 after being asked to leave Lowell Observatory in Flagstaff, Hughes said.

Douglass had challenged Percevil Lowell's theory that markings on Mars were canals that indicated Martian life.

Douglass then spent many years exploring the cycle of visible sun spots, which indicate fluctuations in energy on the sun's surface. About the same time, Douglass began looking at tree rings for evidence of the sun's activity.

"He was trying to find something on Earth that would provide a natural record," Hughes said.

Douglass became the UA's first astronomy professor, but he never stopped looking for the connection between tree rings and sun spots, and in 1937, Douglass persuaded the Arizona Board of Regents to create the tree ring lab.

For the next 20 years, Douglass continued his research but died shortly before his sun spot theory was proven.

Today's lab, located under Arizona Stadium, is the largest in the world. It employs seven full-time researchers, about two dozen graduate students and two dozen undergraduate students.

Karen Hansen, anthropology senior, has worked in the lab for two years as part of the Undergraduate Biology Research Program.

"My own research is done with Black Oak from Shaver Lake in California," she said.

Hansen has done field work collecting the tree samples and describes the roar of the chain saws as the most exciting part of the collection process.

The science behind the dating is a multi-step process:

� It begins with collecting samples, preferably from trees whose planting date or cutting date is known.

� Next, the sample is prepared by cutting out a small section and sanding it to make the rings more visible.

� The sample is put under a microscope and the rings are individually counted and cross dated.

� A computer program then checks the results for accuracy.

� Annual marks are then placed at ten-year intervals.

"The hardest part is having the patience to sit down and measure it all. It can become kind of tedious," Hansen said.

Each ring on the tree represents one growth year, starting in the spring and ending at the onset of winter.

Tree ring records can span thousands of years, making them more accurate for climate prediction than conventional weather reports, said David Meko, research specialist.

In years when sunlight and water are readily available, the tree's rings will be wider, indicating a healthier forest. By sampling many trees across a region, patterns develop that reveal climate patterns.

Climate studies are a predominant research area right now at the lab.

Hughes and Lisa Graumlich, associate professor of dendrochronology, are studying severe, long-term droughts that span up to a thousand years.

But shorter droughts are also studied. This winter's drought is a good example of climate variations.

"To me, it's not a persistent drought, but the big question is whether it will recur," Meko said.

Forest fire research is another feature of the lab. Tracking fire patterns, as measured by the scars the trees carry with them, has shown that El Nino, a disruption of the ocean-atmosphere in the tropical Pacific, is related to forest fires in the Pacific Northwest.

If it is a heavy fire year in the Pacific Northwest, it will be a low fire year in the Southwest, and vice versa, Hughes said.

Since 1937, the lab has also successfully proven the relationship between the sun's activity and tree growth, has dated archaeological sites and is tracking the human dimensions of global change.

The lab presents a public lecture series, "Tree Ring Talks," throughout the semester in Room 104G of the lab, which is under the west side of Arizona Stadium. Lecture days vary, and schedules are posted around campus and on the lab's Internet site, http://www.ltrr.arizona.edu

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